Infrastructure & App Modernization

Infrastructure and app modernization means reshaping how an organization runs its applications so they exploit cloud capabilities (elastic scaling, managed services, and pay-as-you-go cost) instead of merely running in a new place. The rest of this domain is the toolkit for getting there: a set of migration paths decides whether and how each application moves, the compute options decide where the modernized workload runs, and APIs and hybrid/multicloud decide how those workloads connect and span environments. At Cloud Digital Leader altitude the exam tests the business reasoning (why modernize, which path fits a scenario, which product to name) not how to operate any one service.

Google's central message for this domain is that a portfolio is mixed, so each application is assessed individually through application rationalization and assigned the path that fits its business value, risk, and technical state. The named CDL paths form a ladder of rising effort and rising cloud payoff: retain (leave it) and retire (decommission) involve no migration; then rehost (lift and shift, the fastest, least-optimized move), replatform (move and improve), refactor (adopt cloud-native traits like containers and microservices), and reimagine (re-architect and rewrite, the most effort and the fullest benefit). The single most testable skill is mapping the constraint in a stem ("fastest / least change," "move and improve," "become cloud-native," "completely rebuild") onto the right rung, rather than treating reimagine as a universally "best" answer.

Google Cloud's compute products line up by how much of the stack you manage versus how much Google manages for you: Compute Engine virtual machines give operating-system-level control, Google Kubernetes Engine (GKE) runs and orchestrates containers, and the serverless products (Cloud Run and Cloud Run functions) provision, scale, and patch the compute so you supply only code or a container. Because the less infrastructure you manage the less undifferentiated work your team carries, the decision starts at the managed end and steps back toward control only when a constraint forces it: reach for serverless first, move to GKE when you need container orchestration or portability, and drop to a VM for OS-level control or an app that cannot be re-architected. Containers are the pivot of the spectrum: a container packages an app with its dependencies so it runs identically anywhere, which is exactly what makes it portable enough to modernize a legacy app without a full rewrite and the shared deployment unit of both GKE and Cloud Run.

Modernization is not only about where code runs; it is also about how that code is exposed and where it lives across environments. An API (application programming interface) is the published, reusable doorway into a service or dataset, and exposing data and services as APIs opens new business channels and can be monetized directly. Apigee is Google Cloud's managed platform for building, securing, governing, analyzing, and monetizing them across their whole life cycle. Spanning environments is the other axis: a hybrid cloud combines a private/on-premises environment with a public cloud (chosen to keep regulated data on-premises, migrate gradually, or cut latency), while a multicloud uses two or more public clouds (chosen to avoid lock-in, pick best-of-breed services, and add resilience), and GKE Enterprise (formerly Anthos) is the single control plane that manages Kubernetes clusters consistently across all of them.